1. Field of the Invention
This invention relates to improved elastomeric compositions of metal and ammonium neutralized sulfonated elastomeric polymers which are preferentially plasticized with a naphthalene amide at a minimum critical concentration level of at least 8 parts by weight per 100 parts of the metal neutralized elastomeric polymer, wherein the composition has an improved balance of physical and rheological properties, especially at elevated use temperatures. These compositions can be readily processed due to their superior rheological properties on conventional plastic fabrication equipment.
2. Description of the Prior Art
Recently a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728 herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically crosslinked elastomers may be processed like a conventional thermoplastic at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a processable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of U.S. Pat. No. 3,642,728 are readily usable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear as are the improved compositions of the present invention, wherein both improved physical and rheological properties are realized.
U.S. Pat. No. 3,836,511, herein incorporated by reference teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically crosslinked sulfonated elastomers prepared by this process do not exhibit both the improved physical and rheological properties of the compositions of the present invention.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. F. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by the process of U.S. Pat. No. 3,870,841 are not as suitable for the manufacture of high performance elastomeric articles such as footwear formed by an injection molding process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debye, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
The concentrations of the non-volatile plasticizers are limited to an upper concentration of 6-7 parts by weight because with the metal neutralized sulfonated elastomers of this invention, there would be an adverse plasticization of the polymeric backbone. This invention fails to teach, imply or infer the use of an aromatic organic amide as a preferential plasticizer at high concentrations; nor does it recognize that only amides of certain critically selected structures give a particularly advantageous balance of rheological and physical properties. The inventive concept of the present invention clearly teaches the use of selected naphthalene amides as preferential plasticizers at a minimum concentration level of at least about 8 parts by weight thereby achieving not only improvements in rheological properties but also improvements in physical properties. Copending U.S. Ser. No. 855,554 to H. S. Makowski and D. Brenner is directed to the plasticization of sulfonated elastomeric compositions with aliphatic organic amides. In fact, this application implies that the amides as specified in the instant application would not be suitable as plasticizers for sulfonated elastomers. However, it has surprisingly been found that certain critically selected naphthalene amides give a superior balance of rheological and physical properties.